The present invention relates to a throttle control system for opening and closing a throttle valve by controlling driving of a DC motor.
Conventionally, there have been throttle control systems for opening and closing throttle valves by means of actuators, such as DC motors, instead of employing only a direct mechanical linkage between an accelerator pedal and the throttle valve. In such type of the throttle control system, an operational amount of the accelerator pedal is detected by a sensor. On the basis of the detected amount, an open angle command value is derived to drive the DC motor with the open angle command value. Such throttle control system has been disclosed in Japanese Unexamined Patent Publication (Kokai) No. JP-A-61-8434, for example.
However, in the throttle control system employing the DC motor, as set forth above, a problem has been encountered in that, when a difference between an actual open angle of the throttle valve and the open angle command value becomes large, an overshooting of the throttle open angle becomes large.
As a solution for overshooting, there has been proposed in Japanese Unexamined Patent Publication No. JP-A-63-41636, for example, a throttle control system, in which a variation of the open angle command value is rounded to control driving of the DC motor with the rounded open angle command value.
However, even with the technology disclosed in the above-identified publication, satisfactory result in control cannot be obtained. For instance, the disclosed technology is effective in suppressing overshooting under a specific condition, but the degree of rounding becomes excessive in a condition other than the specific condition or rounding is effected even in a conditio where rounding is nor required, since degree of rounding is held constant. This results in degradation of a response characteristics of the throttle valve.